Denture attachment, denture and process for producing the same

ABSTRACT

A dental attachment is embedded in a denture base so as to attach to a keeper made of a soft magnetic material built in a tooth root by magnetic attractive force. The dental attachment comprises an attachment main body which has a magnetic body delivering magnetic attractive force and a cap which covers a head portion located on the opposite side of an attractive surface to attach the keeper of the attachment main body. The cap, made of a non-magnetic material, is installed in the attachment main body so as to be able to move between a contacting position (A) which contacts with the head portion and an extended position (B) which is far from the head portion for a certain distance.

TECHNICAL FIELD

The present invention relates to a dental attachment which is used toembed a denture by magnetic attractive force, and a denture which iscomprised using such a dental attachment, and a method of manufacturingthereof.

BACKGROUND

In dental treatment, as shown in patent document 1, Japanese UnexaminedPatent Application No. 7-136190, because of the easiness of putting onor taking off the denture, various dental attachments utilizing magneticattractive force have been proposed. A dental attachment 91, which has amagnetic body, is, as shown in FIG. 10, embedded in a denture base 810,which is fixed with an artificial tooth 81. On the side of a tooth root,a keeper 92 made of a soft magnetic material is embedded in a root cap82 or an implant (the embodiment is abbreviated) is embedded. Thereforethe denture, which has the dental attachment 91, can be fixed to thekeeper 92 by magnetic attractive force.

As shown FIG. 11 and FIG. 12, in a denture 9 in which are planted aplurality of the artificial teeth 81 in the denture base 810, anartificial tooth 81 a corresponding to the place where the dentalattachment is embedded and an artificial tooth 81 b corresponding to theplace where the dental attachment 91 is not embedded, that is not toface the keeper 92, exist.

Until now, after a denture is made, the denture is put in a oral spacefor about two weeks without the dental attachment (magnetic assembly)built in the denture and when the shrinkage of a gingiva is stabilized,a dentist has combined the dental attachment to the denture. So stressto a gingiva where the dental attachment works is alleviated. But inabout half a year, the gingiva gradually shrinks and modification of thedenture and recombination of the dental attachment are needed.

On the other hand, dentists desire that the dental attachment should becombined with the denture in the making process before dentists work toput the dental attachment into the denture. However, if the combinationis done in the making process, it is unpredictable where and how muchgingiva shrinks. Therefore, if the denture, which is combined with thedental attachment in a conventional making process, is put on for abouta week, stress to the gingiva is concentrated and a strange feeling orache is generated.

In more detail, if the denture which is made and completed on the modelis used, because the denture is not adequately adapted to the oralspace, due to occluding stress, the artificial tooth 81 b and thedenture base 810 supporting it begin to shrink according to the shapechange of the tooth gingiva 88. Meanwhile, the embedded dentalattachment 91 cannot shrink because the keeper 92 and dental attachment91 exist. Therefore, occluding stress is concentrated on the artificialtooth 81 a, which is embedded according to the location of the embeddeddental attachment 91, and it causes a strange feeling or ache to thepatient with the denture 9.

Therefore, especially in the case of combining the dental attachment tothe denture in the making process, development of the dental attachmentwhich has a function to alleviate stress to the gingiva has beendesired. Also, the development of the manufacturing method of thedenture with the dental attachment has been desired.

-   [patent document 1]: Japanese Unexamined Patent Application    Publication No. 7-136190 [patent document 2]: Japanese Unexamined    Utility Model Application Publication No. 6-86715

SUMMARY OF THE INVENTION

The present invention provides a dental attachment which can restrainthe concentration of occluding stress to the part where the dentalattachment is combined even after long use, a denture using that dentalattachment, and its manufacturing method.

A first aspect of the present invention relates to a dental attachmentconfigured to be embedded in a denture base so as to attach to a keepermade of a soft magnetic material and embedded in a tooth root. Thedental attachment comprises an attachment main body which has a magneticbody delivering magnetic attractive force, and a cap covering a headportion which is located on the side opposite to an attractive surfaceto attach the keeper of the attachment main body. The cap is made of anon-magnetic material and engaged to the attachment main body so as tobe able to move between a contacting position which, contacts with thehead portion and an extended position which, is far from the headportion for a certain distance.

The dental attachment of the present invention has, as mentioned above,a cap, which is movable between the connecting position and the extendedposition. Therefore, the whole denture containing the cap can move tothe attachment main body. Therefore, even if the place where a keeperand attachment main body is connected is fixed, the whole denture withthe cap can be moved relative to the keeper within the certain distance.Therefore, even if the denture is made on a model, the denture with thedental attachment can be moved according to the change of the shape ofthe gingiva. Therefore, the denture with the dental attachment canrestrain the concentration of occluding stress even if it is completedon the model in the making process.

Especially, it is not necessary to put the denture in the oral space forabout two weeks to stabilize the shrinkage of the gingiva after theconventional denture without the dental attachment is made. So, it ispossible to complete the denture with the dental attachment on the modelin the making process. Also, the necessity to modify the denture andrecombine the dental attachment is reduced. Yet also it is needless tosay that even in the case that without combining the dental attachmentto the denture in the making process, the dentist combines the dentalattachment to the denture after stabilizing the shrinkage of the gingivain the conventional way, and the necessity to modify the denture andrecombine the dental attachment can be reduced.

The attachment main body (sometimes called a magnet assembly) may haveany well-known structure. Also, the keeper, which is combined to thedental attachment, may have any well-known structure. Furthermore, anattractive surface on the dental attachment, as shown in the followingembodiment, may be flat, may have a convex face, or may have a concaveface with a set curvature.

A second aspect of the present invention is a denture having theabove-described dental attachment embedded in a denture base to attach akeeper made of a soft magnetic material in a tooth root and anartificial tooth planted in the denture base. The dental attachmentincludes an attachment main body which has a magnetic body deliveringmagnetic attractive force and a cap which covers a head portion which islocated on the side opposite to an attractive surface to attach thekeeper of the attachment main body. The cap is made of a non-magneticmaterial and engaged to the attachment main body so as to be able tomove between a contacting position which contacts with the head portionand an extended position which is far from the head portion for acertain distance. The cap is held in the denture base and the attachmentmain body is installed so as to be able to move to the cap.

The denture of the present invention has the constituted dentalattachment. As mentioned above, the denture base holds the cap and theattachment main body is embedded so as to be able to be movable to thecap. Therefore, if at the beginning of use, the attachment main body ismoved forward and set so as to make a gap between the head portion andthe cap, the cap moves forward relative to the attachment main bodyafter use and the placement position of the denture can be changed.Thus, as mentioned above, the denture of the present invention canrestrain the concentration of occluding stress at the combining part ofthe dental attachment.

A third aspect of the present invention is a method of manufacturing theabove described denture having a dental attachment embedded in a denturebase to attach a keeper made of a soft magnetic material in a tooth rootand an artificial tooth planted in the denture base. The dentalattachment includes an attachment main body, which has a magnetic bodydelivering magnetic attractive force and a cap covering a head portion,which is located on the side opposite to an attractive surface to attachthe keeper of the attachment main body. The cap is made of anon-magnetic material and attached to the attachment main body so as tobe able to move between a contacting position, which contacts with thehead portion, and an extended position, which is far from the headportion for a certain distance. Another aspect of the invention includesa process of manufacturing a denture body including the denture base,the artificial tooth planted in the denture base, and a recess so as toinsert the dental attachment in the denture base. This aspect furtherincludes a process of manufacturing a keeper side model which has thekeeper in a casts plaster model which imitates a gingival shapeincluding the tooth root. Also included is a process of setting thedental attachment, in which a spacer with a thickness within the rangein which the cap of the dental attachment can move is installed, and inwhich the dental attachment is installed so that the spacer is contactedto a disk, and in which also the cap of the dental attachment isinstalled in the contacting position. Also included is a process offixing the dental attachment, in which the denture body is covered onthe keeper side model so as to house the dental attachment in the recesswith an adhesive applied inside.

In one example of the method of manufacturing the dental attachment ofthe present invention, at least the process of manufacturing the denturebody, the process of manufacturing the keeper side model, the process ofsetting the dental attachment, and the process of fixing the dentalattachment are performed. One notable part of the manufacturing methodis that before fixing the dental attachment, the spacer is intervened onthe keeper side model on the keeper, and has the setting process of thedental attachment, which is the dental attachment is embedded in thestate of arranging the cap in the connecting position.

By practicing the contacting process of the dental attachment aftersetting the dental attachment using this spacer, the dental attachmentembedded in the denture base has a structure with a gap of the thicknessof the spacer between the keeper and attachment main body with the statethat the head portion of the attachment main body abuts against the cap.Therefore, when the denture is put on the denture base of the same shapeas the keeper model and started to be used, the attachment main bodymoves forward relative to the keeper and is magnetically connected withthe keeper when the attachment main body faces to the keeper. Thus, agap of the thickness of the spacer exists between the face of the headportion of the attachment main body and the cap. After that, asmentioned above, the cap moves forward relative to the attachment mainbody using the gap, according to the change of the shape of the gingiva.So, the placement location of the denture changes and the concentrationof occluding stress can be restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the structure of the dental attachment ofthe first embodiment;

FIG. 2 is an illustration of the structure of the denture of the secondembodiment;

FIG. 3 is an illustration of the structure of the denture body of thesecond embodiment;

FIG. 4 is an illustration of the structure of the keeper side model ofthe second embodiment;

FIG. 5 is an illustration showing a state in which the spacer and dentalattachment are set on the keeper side model of the second embodiment;

FIG. 6 is an illustration showing a state of the process of fixing thedental attachment of the second embodiment;

FIG. 7 is an illustration showing a state of beginning to use the dentalattachment actually of the second embodiment;

FIG. 8 is an illustration of the structure of the dental attachment ofthe third embodiment;

FIG. 9 is an illustration showing a state of setting a spacer and dentalattachment on the keeper side model of the fourth embodiment;

FIG. 10 is an illustration of the state of using a dental attachment inthe prior art;

FIG. 11 is an illustration of a denture in the prior art;

FIG. 12 is an illustration of a bad state in the prior art.

DETAILED DESCRIPTION

According to one example of the dental attachment of the presentinvention, it is preferable that the attachment main body includes themagnetic body, a yoke made of the soft magnetic material with a concavepart which has the magnetic body, a disk made of the soft magneticmaterial which is installed so as to close a opening part of the concavepart with the magnetic body housed in the concave part, and ring shapedcontacting part made of the non-magnetic material which connects thedisk and the yoke, and the cap is covered on the head portion which islocated on the opposite side to the opening part of the yoke. In thiscase, the yoke, the disk and the ring shaped connecting part betweenthese can form an ideal magnetic circuit and magnetic force of themagnetic body can be utilized efficiently.

The non-magnetic material constituting the yoke can be various softmagnetic materials, for instance, 17Cr stainless steel, 17Cr-2Mostainless steel, and 19Cr-2Mo stainless steel are preferable. These aresuperior in non-corrosion and can improve the endurance. Also, as thesoft magnetic material for the disk, various soft magnetic materials areavailable and the same materials as the yoke can be used. Still, theconnection of the disk and the yoke is practiced on the ring shapedconnecting part made of the non-magnetic material. As a specificconnecting method, welding is applicable. Also, as the magnetic bodybuilt in the yoke, a magnet with high magneto motive force per unitvolume is used. Specifically, for instance, Sm—Co based, Nd—Fe—B based,or rare earth magnets with high-energy product are preferable.

Further, it is preferable that the attachment main body has collarsprotruding radially outward from an outer peripheral surface thereof,and the cap has a bottom portion which faces the head portion of theattachment main body and a lateral portion which faces the outerperipheral surface of the attachment main body and covers the collars,and the lateral portion has a protruding part protruding inward to theouter peripheral surface of the yoke and the protruding part and thecollars are engaged when the cap is located at the extended position. Bythis structure, relative movement between the cap and the attachmentmain body is possible and the moving distance between the collars andthe inward protruding part can be easily controlled by attaching them.

Further, it is preferable that the outer peripheral surface of thelateral portion of the cap has a tapered surface reducing radially awayfrom the bottom portion and/or an outward-protruding part. In this case,when the denture is held in the denture base, the taper face or an outerprotruding part bites and delivers the undercut effect, so the attachingstrength of both can be improved.

Further, it is preferable that the cap is made of synthetic resin. Inthis case, by using flexibility of the synthetic resin constituting thecap, the operation to attach with the attachment main body can be doneeasily and the manufacturing becomes simpler. As the synthetic resin,for instance, POM (polyoxymethylene), PE (polyethylene), PET(polyethylene terephthalate) etc. can be used.

Next, according to the third aspect of the invention, it is preferablethat the spacer is made of a permanent magnet or the soft magneticmaterial. In this case, when the spacer is equipped on the keeper, thelocation between both can be maintained stably, and also when the dentalattachment is equipped on the spacer, the location between both can bemaintained stably. Therefore, afterward the process of fixing the dentalattachment can be stably done.

Embodiment 1

A first embodiment of a dental attachment of the present invention isexplained using FIG. 1. A dental attachment 1 of this example is, asshown in FIG. 1, a dental attachment which is embedded in a denture baseso as to be conjugated to a keeper 92 made of a soft magnetic materialin a tooth root by magnetic attractive force.

The dental attachment 1 includes an attachment main body 100, which hasa magnetic body 10 delivering magnetic attractive force and a cap 2covering a head portion 112 which is located on the side opposite to anattractive surface 105 to attach the keeper 92 of the attachment mainbody 100. The cap 2, made of a non-magnetic material and attached to theattachment main body 100 so as to be able to move between a connectingposition (A) which contacts with the head portion 112 and an extendedposition (B) which is far from the head portion for a certain distance.

The attachment main body 100 includes, as shown in FIG. 1 the magneticbody 10 delivering magnetic attractive force, a yoke 11 made of the softmagnetic material which has a recess 110 housing the magnetic body 10, adisk 12 which covers an opening part of the recess 110 with the magneticbody 10 housed in the recess, and a ring shaped connecting part 19, madeof the non-magnetic material, which connects the disk 12 with the yoke11. The cap 2 covers the head portion 112 which is the opposite side tothe opening part of the yoke 11.

As shown in FIG. 1, the yoke 11 of the dental attachment in thisembodiment is almost disk shaped and has collars 115 protruding radiallyoutward from the outer peripheral surface 114. In the depictedembodiment, collars 115 are present all over the outer peripheralsurface 114 at the edge of the head portion 112. However, collars 115can be made, for instance, at circumferentially plural separatedlocations.

Also, the yoke 11 is made of the soft magnetic material,19Cr-2Mo-0.2Ti—Fe, and made by machining. The yoke 11 has the recess 110to house the magnetic body 10 by machining. The inner diameter of thisrecess 110 corresponds to the outer diameter of the magnetic body 10described later. Also, the corner of the outer periphery of the face,which has the recess 110, a taper shaped chamfer 118 is shown.

In the depicted sample, the magnetic body 10 is made of Nd—Fe—B basedpermanent magnet, (BH)max=42MGOe. The disk 12 is a circular disk made ofthe soft magnetic material, 19Cr-2Mo-0.2Ti—Fe, for example. After themagnetic body 10 is inserted in the recess 110 of the yoke 11, the disk12 is inserted and the outer peripheral thereof is welded to the yoke 11with the ring shaped connecting part 19 made of the non-magneticmaterial.

The cap 2 has a bottom portion 21 which faces the head portion 112 ofthe yoke 11 and a lateral portion 22 which faces the outer peripheralsurface 114 and covers the collars 115. The lateral portion 22 has aprotruding part 225 protruding inward to the outer peripheral surface114 of the yoke 11 and the protruding part and the collars 115 areengaged when the cap 2 is located at the extended position (B).

Also, the cap 2 has, as shown in the same FIG, a taper face 226 whichhas a smaller diameter as it is further away from the bottom portion 21at the outer peripheral face of the lateral portion 22. In addition, thecap 2 is made of POM (polyoxymethylene) and mounted on the yoke 11 fromthe side of the head portion 112 of the yoke 11.

The obtained dental attachment 1 has the cap 2, which is movable betweenthe connecting part (A) and the extended part (B), and is structured tobe changeable to the relative position between the cap 2 and the yoke11. Because of this structure, the denture with the cap 2 attached inthe denture base can change the relative position of the whole dentureto the yoke 11 (the attachment main body 100), and excellent operatingeffects can be obtained.

Embodiment 2

In the present example, as shown in FIGS. 2-5, a denture which is madeby using the dental attachment of embodiment 1, and the manufacturingmethod, are explained. A denture 3 of the present embodiment consists,as shown in FIG. 2, of an artificial tooth 32 planted in a denture base31 and the dental attachment 1 of embodiment 1 in the denture base 31.The cap 2 is held in the denture base 31 and the yoke 11 (the attachmentmain body 100) can be movable to the cap 2.

The first step to manufacture this denture is, as shown in FIG. 3, theartificial tooth 32 is planted in the denture base 31 and a denture body30 which has a recess 35 to insert the dental attachment 1 in thedenture base 31 is manufactured. Also, as shown in FIG. 4, a keeper sidemodel 4 which is embedded a keeper 92 in a casts plaster model 41 whichimitates the gingival shape including a tooth root part to install adenture 3 is manufactured. The manufacturing process of this keeper sidemodel can be done before or after the manufacturing process of thedenture body and both process can be done in parallel.

Also, in the process of manufacturing the denture body or the keeperside model, the process of impression taking which transfers the shapeof the gingiva including the tooth root part to install the denture isneeded. Using prior instant adhesive or gypsum can do the process ofimpression taking.

Next, as shown in FIG. 5, preparing a disk shaped spacer 5 which is madeof a ferrite magnet and has almost the same thickness of the movingdistance of the cap 2 of the dental attachment 1, the setting process ofthe dental attachment is done. Specifically, as shown in the same FIG,first, the spacer 5 is installed on the keeper 92 of the keeper sidemodel 4, and on it, the dental attachment 1 on which is installed thecap 2 at the connecting position is installed. At this time, the disk 12is connected with the spacer 5. In the present example, as mentionedabove, the spacer 5 is made of the permanent magnet, so the keeper 92,the spacer 5 and the dental attachment 1 are stably installed.

Next, as shown in FIG. 6, an adhesive 310 is applied inside the recess35 of the denture body 30 and the process of fixing the dentalattachment which covers the keeper side model 4 with the denture body 30in order to house the dental attachment 1 in the recess 35 is conducted.Thus, as shown in the same FIG, the cap 2 of the dental attachment 1 isattached in the recess 35 with the adhesive 310, completing the denture3 which has the dental attachment 1.

In the obtained denture 3, the cap 2 of the installed dental attachment1 is attached and the yoke 11 (the attachment main body 100) is held tobe movable to the cap 2. The starting point of the yoke 11 is set at theadvanced point of the thickness of the spacer 5 from the connectingpoint of the yoke 11 with the cap 2, where the yoke 11 connects with thekeeper 92. Therefore, as shown in FIG. 7, when the keeper 92 is embeddedin a real gingiva 88, which is an original of the keeper side model 4,and the denture 3 is put on it, as shown in the same FIG, the yoke 11advances relative to the cap 2 and contacts the keeper 92 and isconnected. Therefore, at the starting step of usage, a certain amount ofa gap C is made between the cap 2 and the yoke 11 and it become a spacewhich adapts to the subsequent change over time.

That is, in the case that the gingiva 88 begins to shrink, the denturebase 31 also begins to shrink. At this time, the dental attachment 1 ofthe present example, as mentioned above, can move relatively so as toshrink the gap C between the yoke 11 and the cap 2. Therefore, thedenture 3 can follow the change of the gingiva 88's shrinking and moveto a suitable position. Therefore, in the denture 3 of the presentembodiment, even in the case that the gingiva 88 etc. is changed bytime, the concentration of occluding stress on the combining part of thedental attachment can be restrained.

As the denture 3, a denture with a plurality of artificial teeth isespecially effective, but a denture with only one artificial tooth 32can also be excellently effective to deliver the operating effect of thedental attachment 1.

Embodiment 3

The present example is an example of changing the shape etc. of thedental attachment of FIG. 8 and embodiment 1. As shown in FIG. 8, first,an attractive surface 106 is made of a concave surface (spherical face)of an attachment main body 100. As a keeper 92 facing the attachmentmain body 100, an absorbed surface 926 which is made of a convex surface(spherical face) and can be attached to an attractive surface 106 isadopted. The keeper 92 has a post 928 which is extended from the backcenter on the opposite side of the absorbed surface 926.

The cap 2 which covers the head portion 112 of the attachment main body100 has cap collars 228 protruding outward at all outer peripheralsurfaces of a lateral portion 22. In other respects of the structure isthe same as embodiment 1.

The dental attachment of the present example, which has the concaveattractive surface 106 as mentioned above, can be used in combinationwith the keeper 92 which has the convex absorbed surface 926. Therefore,the attaching condition of the attractive surface 106 and the absorbedsurface 926 is maintained and can be inclined from the startingcondition. For some kinds of the dentures, adopting this structure isvery effective.

In the present example, the cap 2 has the cap collars 228. Thus, whenthe cap 2 is connected to a denture base 31 with an adhesive 310, thecap collars 228 is embedded in the adhesive 310 and the connectingstrength between the cap 2 and the denture base 31 can be improved.However, the cap collars 228 need not be made all around and a shapewith at least one radially protruding part is possible. It also obtainsthe same operating effect as embodiment 1.

Embodiment 4

In the present example, as shown in FIG. 9, the manufacturing method ofa denture is explained by using the dental attachment of embodiment 3.The manufacturing method of the present example, which is basically thesame as embodiment 2, is changed in the shape and materials of a spacer52. That is, first, like embodiment 2, a process of manufacturing adenture body 30 which makes the denture body 30 and a process ofmanufacturing a keeper side model which makes a keeper side model 4embeds a keeper 92 in a casts plaster model 41 is performed.

Next, as shown in FIG. 9, a process of setting the dental attachment isperformed by using the disk shaped spacer 52 which is made of the softmagnetic material, 19Cr-2Mo-0.2Ti, and has the thickness of about thesame as the moving distance of the cap 2 of the dental attachment 1 andhas a spherical shape with the same curvature as the attractive surface106 of the attachment main body 100 and the absorbed surface 926 of thekeeper 92. The spacer 52 and the absorbed surface 926 are connected withan adhesive. The process afterward is the same as embodiment 2.

As mentioned above, in the present example, the dental attachment, whichhas the concave attractive surface 106, can be easily installed in thedenture body 30 by using the disk shaped spacer 52 with spherical shape.It also obtains the same operating effect as embodiment 2.

1. A dental attachment configured to be embedded in a denture base so asto attach to a keeper by a magnetic attractive force, the keeperincluding a soft magnetic material and embedded in a tooth root,comprising: an attachment main body including a magnetic body deliveringmagnetic attractive force; and a cap covering a head portion of theattachment main body and located on a side of the magnetic body oppositeto an attractive surface that attaches to the keeper, wherein the capincludes a non-magnetic material and is coupled to the attachment mainbody so as to be configured to move, while remaining coupled to theattachment main body, between a contacting position (A) at which the capis in contact with the head portion and an extended position (B) spacedfrom the contacting position (A) by a distance, a space being providedbetween the head portion and the cap, in the extended position, whereinthe attachment main body further includes a yoke, a portion of the outerperipheral surface of the yoke being straight and without a taper, theyoke including soft magnetic material with a concave part whichaccommodates the magnetic body, a disk including soft magnetic materialwhich is installed so as to close an opening part of the concave partwhile the magnetic body is housed in the concave part, and a ring shapedcontacting part including the non-magnetic material which connects thedisk and the yoke, wherein the cap covers the head portion, which islocated on an opposite side of the yoke to the opening part of theconcave part of the yoke, wherein the yoke has a collar and acylindrical outer peripheral surface, said collar protrudes radiallyoutward from the cylindrical outer peripheral surface of the yoke at theedge of the head portion of the yoke, and the cap includes a bottomportion, which faces the head portion of the yoke, and a lateralportion, which faces the cylindrical outer peripheral surface of theyoke and covers the collar, and the lateral portion includes aprotruding part protruding inward to the cylindrical outer peripheralsurface of the yoke, and the protruding part and the collar are engagedwhen the cap is located at the extended position (B) and said protrudingpart and said collar are not engaged when said cap is located at saidcontacting position (A), and wherein the cap is configured to move,without bias generated by the dental attachment, from the extendedposition (B) to the contacting position (A) and vice versa.
 2. Thedental attachment according to claim 1, wherein an outer peripheralsurface of the lateral portion of the cap includes a tapered surfacereducing radially away from the bottom portion and/or anoutward-protruding part.
 3. The dental attachment according to claim 1,wherein the cap includes synthetic resin.
 4. The dental attachmentaccording to claim 1, wherein the cap is configured to freely move fromthe extended position (B) to the contacting position (A) and vice versaby movement along the portion of the yoke that is straight.
 5. Thedental attachment according to claim 4, wherein the yoke includes atapered portion, and the portion of the yoke that is straight ispositioned between the tapered portion and the collar.
 6. A dentalattachment configured to be embedded in a denture base so as to attachto a keeper by a magnetic attractive force, the keeper including a softmagnetic material and embedded in a tooth root, comprising: anattachment main body including a magnetic body delivering magneticattractive force; and a cap covering a head portion of the attachmentmain body and located on a side of the magnetic body opposite to anattractive surface that attaches to the keeper, wherein the cap includesa non-magnetic material and is coupled to the attachment main body so asto be configured to move, while remaining coupled to the attachment mainbody, between a contacting position (A) at which the cap is in contactwith the head portion and an extended position (B) spaced from thecontacting position (A) by a distance, a space being provided betweenthe head portion and the cap, in the extended position, wherein theattachment main body further includes a yoke, a portion of the outerperipheral surface of the yoke being straight and without a taper, theyoke including soft magnetic material with a concave part whichaccommodates the magnetic body, a disk including soft magnetic materialwhich is installed so as to close an opening part of the concave partwhile the magnetic body is housed in the concave part, and a ring shapedcontacting part including the non-magnetic material which connects thedisk and the yoke, wherein the cap covers the head portion, which islocated on an opposite side of the yoke to the opening part of theconcave part of the yoke, wherein the yoke has a collar and acylindrical outer peripheral surface, said collar protrudes radiallyoutward from the cylindrical outer peripheral surface of the yoke at theedge of the head portion of the yoke, and the cap includes a bottomportion, which faces the head portion of the yoke, and a lateralportion, which faces the cylindrical outer peripheral surface of theyoke and covers the collar, and the lateral portion includes aprotruding part protruding inward to the cylindrical outer peripheralsurface of the yoke, and the protruding part and the collar are engagedwhen the cap is located at the extended position (B) and said protrudingpart and said collar are not engaged when said cap is located at saidcontacting position (A), and wherein the cap is configured to move toadjust to a gum line from the extended position (B) to the contactingposition (A) and vice versa.
 7. The dental attachment according to claim6, wherein an outer peripheral surface of the lateral portion of the capincludes a tapered surface reducing radially away from the bottomportion and/or an outward-protruding part.
 8. The dental attachmentaccording to claim 6, wherein the cap includes synthetic resin.
 9. Thedental attachment according to claim 6, wherein the cap is configured tofreely move from the extended position (B) to the contacting position(A) and vice versa by movement along the portion of the yoke that isstraight.
 10. The dental attachment according to claim 9, wherein theyoke includes a tapered portion, and the portion of the yoke that isstraight is positioned between the tapered portion and the collar.